No games need eight cores
Indeed, there aren't all that many that can take advantage of two anyway.
Although I am led to believe that any game based on the Quake III engine is supposed to benefit a bit, which would mean that Quake IV games should do so as well.
Crysis is a game that stands to get help from just about ay improvement since it is so resource-hungry, but apart from that the only other game I can think of that would gain anything would be Supreme Commander.
In my own experience, I had SupComm running on a Core 2 Duo and switched over to a Quad 6600 and it ran a lot smoother. Not really a big boost on framerate, but a lot less dips and the dips were shallower as well. All in all, the Quad Core made the game perform more consistently the same, at quite a playable level.
But apart from the above, I can't say that double-quad core gaming is going to be anything to write home about.
And given the trouble the current graphic chip moguls have with putting 2 cards together, I shudder to think of the issues of having to deal with 4 cards is going to be.
Who knows ? Maybe we'll see proper drivers for those monsters once there are actually games that can benefit from it all ?
Like when Duke Nukem Forever comes out.
Whatever century that is.